Vane pump with pressure ramp tracking assist

ABSTRACT

Means for preventing vane &#39;&#39;&#39;&#39;skip&#39;&#39;&#39;&#39; or seperation from the cam surface of a vane pump, at the inner end of the pressure ramp on the cam surface. Flow restricting orifice means are provided for the respective vanes, such that the inward movement of the vane in its rotor slot in the pressure zone causes fluid to be displaced from the inner end of the vane slot through the orifice means, thereby establishing a pressure differential force beneath the vane which resists such inward vane movement. The increased pressure at the inner end of the vane slot is limited by partial release to the pressure port through an opening in the cheek plate, which communicates with the inner ends of the vane slots as the vanes are passing through the pressure zone at those vane positions at which the tracking assist is not advantageous.

United States Patent [1 1 Wilcox VANE PUMP WITH PRESSURE RAMP TRACKING ASSIST [75] Inventor: Jack W. Wilcox, Columbus, Ohio [73] Assignee: Abex Corporation, New York, N.Y.

[22] Filed: May 10, 1972 [21] Appl. No.2 252,006

52 US. Cl. ans/1 [51] lint. Cl. F04c 17/00 [58] Field of Search 418/79, 81, 268, 418/1 [56] References Cited UNITED STATES PATENTS 2,393,223 1/1946 Rosen 418/82 3,255,704 6/1966 Mazur... 418/268 2,738,774 3/1956 Rosen 418/80 3,598,510 8/1971 Aoki 418/81 2,968,252 1/1961 Henning 418/81 2,777,396 1/1957 Adams et al..... 418/81 12/1965 Adams et al [451 Dec. 25, 1973 [5 7 ABSTRACT Means for preventing vane skip or seperation from the cam surface of a vane pump, at the inner end of the pressure ramp on the cam surface. Flow restricting orifice means are provided for the respective vanes, such that the inward movement of the vane in its rotor slot in the pressure zone causes fluid to be displaced from the inner end of the vane slot through the orifice means, thereby establishing a pressure differential force beneath the vane which resists such inward vane movement. The increased pressure at the inner end of the vane slot is limited by partial release to the pressure port through an opening in the cheek plate, which communicates with the inner ends of the vane slots as the vanes are passing through the pressure zone at those vane positions at which the tracking assist is not advantageous.

16 Claims, 6 Drawing Figures PATENTEDDECZS ma SHEET 1 'BF 3 PAIENTEI] [18125 I975 UNDERVANE UNDERVANE PRESSURE TRACKING ASSIST FORCE AT INNER END OF RAMP MIDDLE PORTION OF RAMP RAMP INNER END IO- I L l H START RELIEF PORT END OF PORT CLOSES OF RAMP OPENS RAMP ANGULAR POSITION OF VANE ON PRESSURE RAMP VANE PUMP WITH PRESSURE RAMP TRACKING ASSIST This invention relates to an improvement in hydraulic pumps of the type having rotor and stator members, one of which mounts vanes that engage a cam surface presented by the other member. More particularly, the invention is directed to means for maintaining contact of the vanes with the cam surface in the pressure zone of the pump.

In the most common type of commercial vane pump, the vanes are mounted by the rotor for inward and outward movement in vane slots relative to the axis of the rotor rotation. The tips of the vanes slide over or track on the cam surface of the stator that encircles the rotor.'The cam surface is contoured, or shaped, so that the spacing between it and the rotor periphery varies around the rotor. This so-called pumping space, bounded by the rotor surface, the cam surface, and cheek or port plates on each side of the rotor, is generally regarded as comprising four zones: the pressure zone, the suction zone, a transfer zone (which lies between the suction zone and the pressure zone in the direction of rotation), and a sealing zone (which lies between the pressure zone and the suction zone in the direction of rotation). The variations in cam surfacerotor spacing in these zones cause radial vane movement and consequent changes in the volume of the intervane space or transfer pocket between each pair of vanes.

Each pocket increases in volume in the suction zone and diminishes in volume in the pressure zone. The pocket receives fluid through the suction port as it traverses the suction zone, and transfers the fluid by moving it from the suction zone across the transfer zone to the pressure zone. As the volume of the pocket is reduced in the pressure zone, fluid is expelled from the pocket to a pressure port. The pocket volume decrease in the pressure zone occurs because the cam surface approaches the rotor surface more closely there, and thereby pushes the vane back into its slot. The projection of the vane from the rotor is thus diminished, and the corresponding reduction of pocket volume results in the positive displacement of fluid therein to the outlet or pressure port.

The approach of the cam surface toward the rotor surface across the pressure zone is called the pressure ramp, the term ramp being used to designate an inclined surface, as opposed to an arc of fixed or constant diameter about the rotor axis.

By reason of the fact that the pressure ramp is an inward ramp, it positively displaces the vanes inwardly. At the start of the pressure ramp where the inward vane movement begins, a good contact of the vane tip with the cam surface is obtained, and the vane does not separate from the cam surface. However, vane separation does sometimes occur adjacent the inner end of the pressure ramp, near the area where the ramp blends into the so-called minor diameter portion of the cam surface in the sealing zone. This separation, or skip, can be detected as a bare space on the cam surface, followed by chop marks which are wear or impact dents on the cam surface. These can be seen by the naked eye in severe cases, and under magnification in other instances. The chop marks occur where the vanes, after separation from the cam surface, hit the surface as they regain contact with it, where the pressure ramp flattens out. Such vane tip-cam surface separation presents opportunity for escape of high pressure fluid if the vane skips beyond the sealing point on the minor diameter portion. Moreover, when the vane regains contact with the cam surface there is an impact with resulting wear and noise. The phenomenon occurs at virtually all speeds of operation and is not pressure dependent.

It is believed that pressure ramp skip occurs as a result of inward vane momentum that causes the vane to continue to move inwardly, even where the angulation of the ramp is diminishing. In other words, the skip occurs because the rate of inward vane movement exceeds the apparent rate at which the cam surface approaches the rotor, so that the vane momentarily moves away from the ramp.

This invention is predicated upon means for assisting and improving vane tracking on the pressure ramp, and in particular for ovecoming the skip at the inner end of the pressure ramp. The invention is based upon the provision of means for supplying an outwardly directed extra hydraulic force on the vane at the position where skipping tends to occur, adjacent the inner end of the pressure ramp. This force resists and retards the skipping movement, by blocking or opposing the inward momentum of the vane, so that the vane does not move inwardly beyond the position to which the cam surface actually cams it.

The invention also calls for means for controlling the extra hydraulic force beneath the inner end of the vane, so that the force acts only transiently beneath each vane in the pressure zone where it is needed and desired. It can be limited elsewhere, so that unnecessary vane to cam loading is minimal.

The extra hydraulic force which assists in vane tracking is developed by the displacement of fluid through a flow restricting orifice associated with, and preferably in, each vane. The flow is toward the tip or outer end of the vane, and this flow through the restrictor establishes a higher pressure on an inwardly facing surface of the vane, e.g., below the vane in the vane slot, than at the outer end of the vane. A net outward force is thereby established. The flow restricting orifice is preferably in the form of one or more narrow openings extending between the inner and outer ends of the vane.

Fluid is caused to flow through the restrictor, thereby to establish the force, by the inward movement of the vane into the vane slot. When the pressure ramp pushes the vane inwardly in the slot, trapped fluid in the slot below the vane is displaced upwardly through the orifice, and thereby creates a higher pressure at the inner end of the vane than at the outer end. It is this pressure differential which gives rise to the outward force on the vane that prevents it from skipping, by slowing the rate of inward vane travel where the slope on the pressure ramp becomes less steep.

The orifice can be of various shapes, but it is preferred that it be a sharp orifice formed by a bore portion which is relatively short (in axial dimension) and relatively narrow (in diameter) that connects with a counterbore portion, longer and larger in diameter, that extends the remainder of the distance through the bore. A sharp orifice configuration is highly responsive to vane velocity, and is almost free of the viscosityrelated effects that accompany use of a long bore wherein a major part of the pressure drop is caused by surface drag.

RPM Force, lbs.

The particular area on the cam surface at which vane skip is most pronounced will depend upon its contour. It usually will be at the inner end of the pressure ramp. It is at the area where vane lift-off would otherwise start to occur, that the undervane hydraulic assist is needed.

Since the tracking assist force is dependent upon vane radial velocity, the force will be established wherever fluid is displaced through the orifice by radial vane movement. Such vane movement occurs across the entire pressure ramp, and hence this force could act on the vane across the entire pressure ramp, including areas where it is not needed and would result in extra vane load and wear.

As previously indicated, the invention contemplates, in addition to the restriction for creating the differential force, means for controlling and limiting the excess force at those positions of the vane on the pressure ramp where the force is not needed for tracking assist, and where it would be undesirable.

An orifice sized to provide the desired level of force at the inner end of the pressure ramp, would establish a greater than necessary force at other parts of the pressure ramp where the vane velocity is higher but at which the assist is not desired. If not relieved, this force would peak at a value which would constitute an excessive, or at least unnecessarily high, loading on the vane, and would tend unduly to increase vane tip wear.

In order to limit the peak undervane pressure and the resulting assisting force acting on the vane elsewhere than at the portion of the ramp where it is needed, the invention provides relief port means whereby excess undervane pressure is spilled or relieved where it is not desired, so that an excessively high pressure peak is avoided. The port is closed at the inner end of the ramp so that the necessary pressure force is available to act on the vane at that point at which ramp skipping would otherwise occur.

The relief port is preferably formed in the cheek plate which is at the front face of the rotor, and it communicates with the inner end of the vane slot in the region in which excessive or unnecessary pressure would otherwise exist. The port is connected to the main pressure or outlet port of the pump. The inner end of each vane slot is only transiently in communication with the relief port, as it sweeps by the latter, but this brief communication is sufficient to limit the excess pressure. It is most desirable that the relief port be positioned at that angular location (with respect to the cam surface) where the inward velocity of the vane is the greatest, since no assist is needed at that point and it is at that point that the pressure build-up beneath the vane by flow through the restricting orifice would be the greatest. Since the point of highest vane radial velocity is generally at the middle of the pressure ramp, the relief port is desirably centered there. This central or symmetrical location is especially useful in reversible pumps, wherein the cam ring can be reversed in the body to establish an opposite direction of rotor movement.

The invention can best be further described by reference to the accompanying drawings, which show a preferred embodiment of the invention as incorporated in a radially balanced vane pump having vanes of the twolip type. In the drawings:

FIG. 1 is an axial section of the pump, and is taken on a line through the opposed pressure zones thereof;

FIG. 2 is a plan view of the front cheek plate or port plate, taken along line 2-2 of FIG. 1, illustrating the undervane pressure relief ports, and showing superimposed thereon in dot-dash lines the momentary positions of rotor vane slots;

FIG. 3 is a side elevation, partly broken away, of a vane of the type used in the pump shown in FIG. 1;

FIG. 4 is an end elevation of the vane shown in FIG.

FIG. 5 is an enlarged view of a portion of the cam ring and rotor assembly of the pump, taken along line 55 of FIG. 1; and

FIG. 6 is a diagrammatic illustration showing how the undervane pressure established in accordance with the invention is related to the angular position of the vane on the pressure ramp, and also shows in dashed lines the peak or overpressure which could result in the absence of the undervane pressure relief port.

The invention described and claimed herein is broadly applicable to vane pumps in which both the inner and outer ends of the vanes are exposed to fluid pressure, including pumps which have single lip vanes as well as those which have double lip vanes. The vanes may be biased by hydraulically operated pistons, or by springs. The invention is described hereinafter in relation to a balanced pump having hydraulically operated vanes of the two-lip type, but it should be understood that this is by way of illustration and not limitation.

Referring to FIGS. 1-5, the pump shown there as one type of environment for the invention includes a housing or casing formed by a body casting 1 having a generally cylindrical internal chamber, and an end cap 2 having a recessed shoulder 3, which telescopes into one end of the body and is sealed thereto by an O-ring 4. The body and end cap are connected by bolts, not shown. The end wall 5 of cap 2 has an opening through which the pump operating shaft 6 extends. In cap 2, shaft 6 is supported for rotation by a bearing 7 which is secured against axial movement in the opening. A seal 8 prevents the leakage of fluid along shaft 6. The shaft extends into body 1 from end cap 2, and at its rear or inner end is carried for rotation by a roller bearing 9 mounted within a central bore in the body 1.

The end cap 2 supports and is sealed around a front cheek plate 10, sometimes called a port plate, which has a smooth, flat inner surface 11 that bears against a side or radial face 13 of an annular cam ring or stator 14. On its opposite side surface 17, cam ring 14 bears against a smooth, flat surface 18 of a rear cheek or port plate 19, and holds the latter against an internal shoulder (not shown in FIG. 1) in body I. The cam ring itself, as well as the housing and cam ring together, are sometimes referred to as a stator. Cam ring 14 and the front and rear cheek plates l0, 19 respectively, are clamped together by bolts, not shown. Both cheek plates have central openings through which shaft 6 extends.

A fluid intake passage (not shown in FIG. 1) extends into body 1 and'communicates with a pair of annular channels 23, 24 which encircle the internal cavity within the body. These annular channels 23, 24 distribute fluid from the intake passageway to the suction ports in the cheek plates. The cam ring 14 is supported radially by an annular rib 26 formed in body 1 between the annular channels 23, 24. The cam ring encircles a rotor 28 which is connected to'and driven by shaft 6 through splines 29. The spline joint permits proper running alignment of the rotor between the opposed flat surfaces 11 and 18 of the front and rear cheek plates and 19 respectively. The rotor has a plurality of radial vane slots 31 (see FIG. 5) in each of which a vane 32 is mounted.

The cam ring 14 has an inwardly facing cam surface 34 that is contoured to provide a balanced or symmetrical pump construction in which there are pairs of dia metrically opposite low pressure, inlet or suction zones 37 (see FIG. 5) and high pressure outlets or exhaust zones, one of which is shown at 38 in FIG. 5. Each vane engages the cam surface 34 of the cam ring 14, and the side edges of the vane slide over the smooth flat surfaces 11 and 18 of the front and back cheek plates on opposite sides of the rotor. The pairs of adjacent vanes divide the annular pumping space between the rotor, cam surface, and cheek plates into a series of transfer pockets or intervane spaces, several of which are designated at 40a, 40b, 40c, and 40d in FIG. 5. The intake passageway communicates via the annular channels 23, 24 around cam ring 14, through passages cored in the cheek plates 10 and 19 to paired main suction ports spaced 180 apart in surfaces 11 and 18 thereof. As seen in FIG. 2, two main suction ports 43 and 44 are formed in front cheek plate 10, and they are fed through channel 24. Similar main suction ports (not shown in the drawings) are formed in rear cheek plate 19 and are fed through channel 23. The main suction ports are aligned with the corresponding suction zones 37 in the pumping space between the rotor periphery- 36 and the cam surface 34. Each main suction port is connected by a branch passage (not shown), with an undervane suction port in its cheek plate, such as the port 45 in the front cheek plate 110 The undervane suction ports 45 are radially positioned so that the inner ends 46 of the vane slots 31 will pass across them as the rotor turns. (In FIG. 2 the inner ends 46 of the vane slots are superimposed in phantom on cheek plate surface 11.) The use of undervane suction ports is conventional in the art, and they are shown in conventional form in the drawings; however, it should be understood that the undervane suction ports may be of the specially shaped type shown in the co-pending patent application of Swain and Adams titled Vane Pump Having Extended Undervane Suction Ports, Ser. No. 255,580, filed May 22, 1972. The undervane suction ports do not comprise a part of the invention. A shallow drain slot such as that designated at 47 in FIG. 2 extends radially in the faces 11 and 18 of the respective cheek plates 10 and 19, from the undervane ports 45 thereof, to the central shaft openings. Slot 47 drains fluid from the cavity around shaft 6.

As shown in FIGS. 1 and 2, the front cheek plate 10 includes two diametrically opposed main pressure ports 51 and 52. These ports are generally T-shaped in plan, and they are centered substantially 90 from the main suction ports 43 and 44. They open to the pressure zones 36 between the rotor and the cam surface, and may be provided with conventional bleed slots as indicated at 53. The main pressure ports 51, 52 are connected through internal passages 55, 56 in cheek plate 10 to a fluid outlet or delivery passage 57 in end cap 2, which in turn leads to a fluid outlet or delivery coupling (not shown) that in use is connected to an external hydraulic circuit.

There is associated with each main port 51, 52 in cheek plate 10 a second or relief pressure port 58. Each port 58 is connected through a passageway 59 with the respective pressure passage 55 or 56 in the cheek plate. As seen in FIG. 2, the undervane relief ports 58 may be circular in configuration, and preferably they are substantially centered with respect to the main pressure ports 51, 52 and the pressure zone 38 of the pump. They are positioned radially so that their inner edges are in line with the bottoms of the vane slot inner ends 31. The diameter of each port 56 is preferably less than that of the rounded inner end of the vane slot.

The cam ring may be aligned with respect to the two cheek plates by dowel pins (not shown in the drawings) projecting from its faces 13 and 17. The dowel pins are registrable in holes, one of which is designated at 62 in FIG. 2, in the respective cheek plates 11 and 18, as is known in the art.

In the embodiment shown in the drawings, each vane 32 has a medial groove along its outer edge, as designated at 63. Two lips are'defined on the outer end of each vane, on opposite sides of groove 63. With respect to the direction of rotor rotation indicated by the arrow in FIG. 5, the leading lip of each vane is designated 64 and the trailing lip 65. The inward lead or so-called pressure ramp 67 on cam surface 34 in the pressure zone 38, is evident in FIG. 5. By reason of the inward lead of pressure ramp 67, only the front or leading lip 64 of a vane will engage the ramp in the pressure zone, and the rear or trailing lip 65 of the vane will be spaced inwardly from the pressure ramp in that zone. Conversely, in the suction zone 37, where the cam surface 34 has an outward lead, only the rear or trailing lip 65 of a vane engages the suction ramp 68.

It is known to use either springs or hydraulically operated means to provide an actuating force on each vane that will bias the vane toward the cam surface. The illustrated pump incorporates hydraulic piston biasing means. Use of such pistons for this purpose is known in the art, and they are not part of the invention. Specifically, in rotor 28, a radial bore or cylinder 69 extends inwardly from the inner end 46 of each vane slot 31. The bores 69 are interconnected at their inner ends by an annular pressure chamber 71. Fluid can flow into and out of pressure chamber 71 only through the radial bores 69, the chamber 71 being closed inwardly, as by a sleeve member 72 secured to the rotor. A generally cylindrical piston valve element 73 slides in each radial bore 69. Each piston has an axial bore 74 and its outer end is conically tapered and forms a valve with the inwardly facing surface or inner end 75 of the respective vane. The operation of such hydraulic piston vane biasing means is described in US. Pat. No. 3,223,044, to which reference may be made. The remainder of the inner end surface 75 of each vane (i.e., except at the piston) is exposed to the pressure of fluid in slot end 46, and the resulting pressure force, together with the piston force, urges the vane outwardly.

At least one, and preferably two, flow restricting means designated generally at 77 are provided in each vane and extend from the inwardly facing surface or inner end 75 thereof, radially outwardly to groove 63. The restricting means 77 establish a pressure drop or a differential pressure when fluid flows through it. The restricting means 77 preferably comprises a flow restricting orifice or inner end portion 78 which is relatively short (in the axial direction) and relatively narrow in cross-section, and a connecting passage 79 that has a larger diameter than the restrictor portion 78 and which connects the latter to the top of the vane. By way of example, orifice 78 may be formed by a No. 44 drill, and may have a length of about 0.050 inch, but these values are illustrative and one will depend on the volume of displaced fluid and on the desired force.

The restrictor portion 78 preferably forms a sharp or right angled corner 80 with the inner end 75 of the vane, and has the characteristics of a sharp orifice as that term is understood in the art. As will be described in greater detail hereinafter, fluid flow through the orifice 78 in the direction from the inner end 75 of the vane toward groove 63, creates a pressure differential, the pressure beneath the vane (in the vane slot) being greater than the pressure above the vane (in groove 63).

OPERATION When shaft 6 is driven by a prime mover (not shown), fluid is received into the intervane pockets 40 as they sweep sequentially through suction zone 37. At the same time, fluid is supplied through the undervane suction port 45, into the inner end 46 of the respective vane slot. Thus, in the suction zone the pressures on the inner end outer ends of the vanes are equal and opposed, and are substantially offsetting. The biasing force supplied by the piston 73 holds the vane outwardly and maintains contact with the suction ramp. As the rotor turns (counterclockwise in FIG. and carries the vanes through the transfer zone 41 that lies between the suction and pressure zones, the volume of the pocket does not change greatly, if at all; as a result there is little or no flow through the restrictor 77, and they maintain static balance between the pressures on the inner and outer vane ends. When the vane comes onto the pressure ramp 67, the inward angulation of the ramp exerts a camming force on the leading lip 64 of the vane, and displaces the vane inwardly in its slot. Since the inner end of the vane slot is full of fluid (having been filled in the suction zone), this inward motion must displace fluid from the slot. Prior to the position at which the inner end of the vane slot comes into communication with the undervane relief port 58 in the pressure zone, the only path (excepting minor leakage) for fluid release is through the flow restrictor means 77. Therefore, the inward movement of the vane in its slot causes fluid to flow outwardly through restrictor 77. This creates a higher pressure in the vane slot than at the outer end of the vane in groove 63. This pressure differential acts over the inwardly facing vane surface (except at piston 73), and supplies an extra vane biasing force that supplements the force of the piston.

At the initial portion of the pressure ramp, where the ramp angulation is increasing, the vane is positively cammed inwardly and is being accelerated, so that a pressure assist beneath the vane is not required to maintain vane contact with the cam surface. In order to minimize the vane loading on the pressure ramp at those areas thereof where skipping does not occur, the relief port 58 opens to the vane slot inner end when the vane is moving on the center part of the pressure ramp. This is indicated diagrammatically in FIG. 6, by the legend relief port opens. Absent the control of pressure the relief port provides, the undervane pressure would approach a peak pressure P where the inward vane velocity was the highest (in the middle of the pressure ramp) as indicated by the broken line in FIG. 6. This would lead to unnecessary wear. Provision of the relief port prevents this. A pressure force assist is maintained during the critical portion of the vane travel on the inner end of the pressure ramp, but the peak is cut off" by relief through the undervane port. (The relief port is sized small enought that it does not spill the entire excess pressure beneath the vane.) When the vane appoaches the inner end of the pressure ramp, where the angulation of the latter starts to diminish, the inward momentum of the vane would cause it to skip on the ramp, were it not for the tracking assisting force.

As illustrated diagrammatically in FIG. 6, the trailing edge of pressure port 58 is preferably positioned angularly or timed to close at the inner end of the ramp. The extra pressure force decays as vane velocity drops, but nonetheless is sufficient to prevent the skip.

Positioning of relief port 58 in the middle of the ramp is especially useful in a reversible pump, since the timing of the port opening and closing will be the same for either direction of rotation. Where the pump is not reversible, the port may open even earlier, to release the pressure load on the initial part of the ramp as well.

It is recognized that undervane ports in the pressure zone are shown in U.S. Pat. No. 2,919,651, issued to D. B. Gardiner. There, however, no flow restricting means are provided in the vanes. Since fluid is displaced from the vane slot across the entirety of the pressure ramp, and must have somewhere to go, the cheek plate restrictor consequently must communicate with each slot across the entirety of its travel on the ramp, to accommodate the displaced fluid. This subjects each vane to an extra outward force across the entirety of the ramp even where no tracking assist is needed. The pressure at the center of the ramp is not limited or partially released, and higher wear results.

In the embodiment described, the restrictor means comprises one or more orifices contained wholly within each vane. It will be appreciated by those skilled in the art that restrictor means may alternatively be provided in the rotor, or at the edge of the vanes, as by a narrow slot or groove formed in the vane which is closed by the cheek plate against which the vane slides. Such means are comprehended by the term flow restricting means used in the claims.

The short orificeconfiguration illustrated is desirable and is preferred (in contrast to a long restrictor) because it is freer from oil acceleration effects.

While the invention has been described in relation to a particularly preferred embodiment, those skilled in the art will understand from the foregoing specification that it comprehends alternative embodiments, within the scope of the claims which follow.

I claim:

1. A method of peventing vane skip in the operation of a vane pump where the vanes are moving across the inner end of a pressure ramp therein, said method comprising,

displacing fluid from the inner end of the vane slot by inward movement of the vane on the pressure ramp,

directing the displaced fluid through a flow restricting orifice thereby to establish a pressure differential across said orifice,

applying the higher pressure across said orifice to an inwardly facing surface of the vane thereby to oppose the inward vane movement,

and limiting the higher pressure on said inwardly facing surface prior to the position at which the respective vane comes onto the inner end of the pressure ramp. 2. The method of claim 1 wherein the said limiting of pressure is timed to occur while the respective vane is traversing the central portion of the pressure ramp.

3. The method of claim 1 wherein said higher pressure is applied to the inner end of the respective vane. 4. In a vane type hydraulic pump having rotor and stator members, vanes mounted in vane slots in one member for engaging a cam surface presented by the other member, the cam surface including a pressure ramp in a pressure zone of the pump which ramp cams the vanes into their respective slots as they move relatively thereover,

the improvement comprising, flow restricting means for each said vane through which fluid in the inner end of the slot is displaced when the vane is moved into its slot, such displacement establishing a pressure differential force on an inwardly facing surface of the vane opposing the inward vane movement, and a relief port communicating with said inwardly facing surface for controlling the pressure thereon during movement of the vane along the pressure ramp,

said relief port positioned to communicate with the inner end of a vane slot only when the respective vane is traversing a central portion of the pressure ramp.

5. The improvement of claim 1 wherein said relief port communicates with a pressure port of the pump.

6. The improvement of claim 5 wherein said relief port is in the form of an aperturein a cheek plate and has a diameter smaller than'that of the inner end of a vane slot.

7. The improvement of claim 1 wherein said flow restricting means comprises a passage extending through the vane between the inner and outer ends thereof.

8. The improvement of claim 7 wherein said passage includes a sharp orifice which is defined by a bore that meets an end surface of the vane at substantially a right angle.

9. In a hydraulic vane pumphaving a rotor carrying vanes that are slidable in vane slots therein, a stator presenting a cam surface engaged by the outer ends of the vanes as the rotor rotates, the cam surface including a pressure ramp in a pressure zone of the pump which ramp cams the vanes inwardly in their respective slots as they traverse it, and a cheek plate presenting a pressure port opening to the space between the rotor and cam surface in the pressure zone,

the improvement comprising,

flow restricting means in each vane providing a path for restricted flow of fluid in an outward direction to the outer end of the vane from an inwardly facing surface thereof, said flow restricting means being sized so that flow therethrough resulting from inward vane movement on the pressure ramp will establish a pessure differential force on said inwardly facing surface,

and a relief port in said cheek plate, said relief port connected to said pressure port and positioned to communicate with the said inwardly facing surface where the inward velocity of the vane is at its highest value, but not when the vane is at the inner end of the pressure ramp.

10. The improvement of claim 9 where said relief port communicates with said inwardly facing surfae where the respective vane is moving on the central part of the pressure ramp.

ll. The improvement of claim 9 wherein said inwardly facing surface is the inner end of the vane.

12. The improvement of claim 11 wherein said relief port is positioned to communicate with the inner end of a vane slot.

13. The improvement of claim 9 wherein the flow restricting means is at least one restricted passage extending radially through the vane, between the inner and outer ends thereof.

14. The improvement of claim 13 wherein the passage includes a sharp, short orifice.

115. A vane for use in a hydraulic pump of the type having a rotor carrying vanes that are slidable in vane slots therein, a stator presenting a cam surface engaged by the outer ends of the vanes as the rotor turns, the cam surface including a ramp in a pressure zone of the pump which ramp cams each vane inwardly in its respective slot as it traverses the ramp, and a check plate presenting a pressure port opening to the space between the rotor and cam surface in the pressure zone.

said vane having flow restricting means associated with it providing a path for restricted flow of fluid between the inner and outer ends of the vane, said flow restricting means being sized so that flow therethrough resulting from inward vane movement on the said ramp will establish a pressure differential force beneath the vane of magnitude sufficient to prevent skip at the inner end of the pressure ramp,

said flow restricting means being provided in the form of a passage including a sharp, short orifice, flow across which establishes the pressure drop, and a larger diameter passage portion connecting said sharp orifice to an opposite edge of the vane.

16. The vane of claim 15 wherein said passage is a radial passage in the vane, and said orifice is adjacent the inner edge of the vane, and meets said inner edge at a right angle.

t: t a 

1. A method of peventing vane skip in the operation of a vane pump where the vanes are moving across the inner end of a pressure ramp therein, said method comprising, displacing fluid from the inner end of the vane slot by inward movement of the vane on the pressure ramp, directing the displaced fluid through a flow restricting orifice thereby to establish a pressure differential across said orifice, applying the higher pressure across said orifice to an inwardly facing surface of the vane thereby to oppose the inward vane movement, and limiting the higher pressure on said inwardly facing surface prior to the position at which the respective vane comes onto the inner end of the pressure ramp.
 2. The method of claim 1 wherein the said limiting of pressure is timed to occur while the respective vane is traversing the central portion of the pressure ramp.
 3. The method of claim 1 wherein said higher pressure is applied to the inner end of the respective vane.
 4. In a vane type hydraulic pump having rotor and stator members, vanes mounted in vane slots in one member for engaging a cam surface presented by the other member, the cam surface including a pressure ramp in a pressure zone of the pump which ramp cams the vanes into their respective slots as they move relatively thereover, the improvement comprising, flow restricting means for each said vane through which fluid in the inner end of the slot is displaced when the vane is moved into its slot, such displacement establishing a pressure differential force on an inwardly facing surface of the vane opposing the inward vane movement, and a relief port communicating with said inwardly facing surface for controlling the pressure thereon during movement of the vane along the pressure ramp, said relief port positioned to communicate with the inner end of a vane slot only when the respective vane is traversing a central portion of the pressure ramp.
 5. The improvement of claim 1 wherein said relief port communicates with a pressure port of the pump.
 6. The improvement of claim 5 wherein said relief port is in the form of an aperture in a cheek plate and has a diameter smaller than that of the inner end of a vane slot.
 7. The improvement of claim 1 wherein said flow restricting means comprises a passage extending through the vane between the inner and outer ends thereof.
 8. The improvement of claim 7 wherein said passage includes a sharp orifice which is defined by a bore that meets an end surface of the vane at substantially a right angle.
 9. In a hydraulic vane pump having a rotor carrying vanes that are slidable in vane slots therein, a stator presenting a cam surface engaged by the outer ends of the vanes as the rotor rotates, the cam surface including a pressure ramp in a pressure zone of the pump which ramp cams the vanes inwardly in their respective slots as they traverse it, and a cheek plate presenting a pressure port opening to the space between the rotor and cam surface in the pressure zone, the improvement comprising, flow restricting means in each vane providing a path for restricted flow of fluid in an outward direction to the outer end of the vane from an inwardly facing surface thereof, said flow restricting means being sized so that flow therethrough resulting from inward vane movement on the pressure ramp will establish a pessure differential force on said inwardly facing surface, and a relief port in said cheek plate, said relief port connected to said pressure port and positioned to communicate with the said inwardly facing surface where the inward velocity of the vane is at its highest value, but not when the vane is at the inner end of the pressure ramp.
 10. The improvement of claim 9 where said relief port communicates with said inwardly facing surfae where the respective vane is moving on the central part of the pressure ramp.
 11. The improvement of claim 9 wherein said inwardly facing surface is the inner end of the vane.
 12. The improvement of claim 11 wherein said relief port is positioned to communicate with the inner end of a vane slot.
 13. The improvement of claim 9 wherein the flow restricting means is at least one restricted passage extending radially through the vane, between the inner and outer ends thereof.
 14. The improvement of claim 13 wherein the passage includes a sharp, short orifice.
 15. A vane for use in a hydraulic pump of the type having a rotor carrying vanes that are slidable in vane slots therein, a stator presenting a cam surface engaged by the outer ends of the vanes as the rotor turns, the cam surface including a ramp in a pressure zone of the pump which ramp cams each vane inwardly in its respective slot as it traverses the ramp, and a cheek plate presenting a pressure port opening to the space between the rotor and cam surface in the pressure zone. said vane having flow restricting means associated with it providing a path for restricted flow of fluid between the inner and outer ends of the vane, said flow restricting means being sized so that flow therethrough resulting from inward vane movement on the said ramp will establish a pressure differential force beneath the vane of magnitude sufficient to prevent skip at the inner end of the pressure ramp, said flow restricting means being provided in the form of a passage including a sharp, short orifice, flow across which establishes the pressure drop, and a larger diameter passage portion connecting said sharp orifice to an opposite edge of the vane.
 16. The vane of claim 15 wherein said passage is a radial passage in the vane, and said orifice is adjacent the inner edge of the vane, and meets said inner edge at a right angle. 